The present invention relates to a rotation sensor such as a vehicle wheel speed sensor or an engine revolution sensor.
FIG. 8 shows a conventional wheel speed sensor P. It includes a detector X mounted on a circuit board 3 which is in turn carried on a resin holder 2. With the detector X mounted on the holder 2, the holder 2 is inserted into a cylindrical casing 1 having open and closed ends from its open end 1a until a base portion 2a of the holder 2 closes the open end of the casing 1. A pair of lead wires 9 extending from the detector X are each connected to one of a pair of relay terminals 5 which extend through the base portion 2a of the holder 2 and protrudes from its outer end face. The relay terminals 5 have their protruding ends connected to an output cable 6. A cover 4 is formed by molding a resin to completely conceal the portion of the holder 2 protruding from the open end 1a of the casing 1 and to embed therein the protruding ends of the relay terminals 5 and the portion of the cable 6 connected to the terminals 5.
The detector X typically comprises an IC chip for detecting magnetic fields and electronic parts (circuit) for controlling (as disclosed in JP Patent publication 2002-257840, FIG. 4) or comprises an electromagnetic pickup including a pole piece provided inside of a bobbin on which a coil is wound, and a magnet provided rearwardly of the pole piece (as disclosed in the above publication, FIG. 1).
As shown in FIG. 8, the wheel speed sensor P is mounted on a mounting member A with its detector X opposing a rotary member B to be detected. The detector X picks up any change in the magnetic field produced from the rotary member B when the rotary member B rotates, and converts the change in the magnetic field to electrical signals which are transferred to a control device through the relay terminals 5 and the output cable 6. The rotary member B is a ferromagnetic pulse ring having teeth similar to gear teeth on the radially outer periphery thereof, or a magnet pulse ring having its radially outer periphery magnetized such that North poles and South poles circumferentially alternate with each other.
As today's motor vehicles are increasingly sophisticated, it is necessary to densely pack various devices and components, besides wheel speed sensors, in a limited space. Thus, smaller wheel speed sensors are required. To reduce the size of a wheel speed sensor, its components have to be arranged closer to one another. This increases the possibility of interference of each component with other components.
For example, the pair of lead wires 9 extending from the detector X tend to interfere with each other at their connecting portions 9a connected to the relay terminals 5. That is, if the holder 2 has a sufficiently large diameter as in the case of a conventional wheel speed sensor P shown in FIG. 9A, the connecting portions 9a can be sufficiently spaced from each other as shown by the letter L in FIG. 9A. But in a smaller wheel speed sensor P shown in FIG. 9B, it is necessary to correspondingly reduce the diameter of the holder 2 and the distance L between the connecting portions 9a. 
The smaller the distance L between the connecting portions 9a, the greater the chance of poor insulation between the connecting portions 9a. For example, the connecting portions 9a may be electrically connected together through protrusions c of welded portions due to excessive welding as shown in FIG. 10A, or a protrusion d of a soldered portion as shown in FIG. 10B, or due to misalignment of the lead wires 9 and the relay terminals 5 as shown in FIG. 10C.
Poor insulation of the connecting portions 9a tends to make the wheel speed sensor P defective.
An object of the present invention is to provide a rotation sensor wherein the connecting portions of a pair of leads extending from a detector that are connected to relay terminals are reliably insulated from each other.